​
Overview

The DATE_TRUNC() function truncates a timestamp, timestamp with time zone or interval value to the specified precision, effectively rounding down the value to the start of the given time unit. The return type matches the input type.

​
Syntax

The syntax for using the DATE_TRUNC() function is as follows: 
DATE_TRUNC(field, source)

​
Parameters

  • field: The unit of time used to truncate the source value. It accepts text inputs and is case-insensitive
  • source: The value you want to truncate. It can be INTERVAL, TIMESTAMP or TIMESTAMP WITH TIME ZONE
  • time_zone (applicable for the second syntax option): The time zone for the operation. It accepts text input

​
Fields

Below is a list of supported values to specify the fields param in DATE_TRUNC() syntax.
  • microseconds
  • milliseconds
  • second
  • minute
  • hour
  • day
  • week
  • month
  • quarter
  • year
  • decade
  • century
  • millennium
Some fields like microseconds and milliseconds are supported only for interval types.

​
Examples

​
Truncating to Year

This example truncates the timestamp to the year level. 
select DATE_TRUNC('year', '1911-12-02 19:40:00'::timestamp);
The timestamp **“1911-12-02 19:40:00” **has been truncated to 1911, with the month and day set to January 1st. 
         date_trunc         
----------------------------
 1911-01-01 00:00:00.000000

​
Truncating to Day

This query truncates the timestamp “1911-12-02 19:40:00” to the day level. 
select DATE_TRUNC('day', '1911-12-02 19:40:00'::timestamp);
The timestamp has been truncated to the same day, year, month, and day components. 
        date_trunc         
----------------------------
 1911-12-02 00:00:00.000000

​
Truncating to Week

This query truncates the timestamp “1911-12-02 19:40:00” to the week level. 
select DATE_TRUNC('week', '1911-12-02 19:40:00'::timestamp);
The timestamp has been truncated to the start of the week containing the date, which is Monday, November 27, 1911, at 00:00:00. 
        date_trunc         
----------------------------
 1911-11-27 00:00:00.000000

​
Truncating to Quarter

This query truncates the timestamp “1911-12-02 19:40:00” to the quarter level. 
select DATE_TRUNC('quarter', '1911-12-02 19:40:00'::timestamp);
The timestamp is truncated to the start of the quarter. The month and day are set to the first month and first day of the quarter, with time components reset to zero. 
        date_trunc         
----------------------------
 1911-10-01 00:00:00.000000

​
Truncating to Hour

This query truncates the interval “15 hours 10 minutes” to the hour precision. 
select DATE_TRUNC('hour', '15 hour 10 minutes'::interval);
The minutes and seconds components are set to zero, resulting in an interval of exactly 15 hours. 
   date_trunc    
-----------------
 15:00:00.000000

​
Truncating to Quarter (Interval)

This query truncates the interval “16 years 4 months” to the quarter-year level. 
select DATE_TRUNC('quarter', '16 years 4 months'::interval);
The interval is truncated to the nearest quarter-year unit. The months components is adjusted to the start of the quarter. Since each quarter consists of 3 months, 4 months is truncated down to 3 months, resulting in: 
   date_trunc    
-----------------
 16 years 3 mons